This invention relates to hand operable brake mechanisms and particularly, to a hand brake mechanisms for railway cars.
Railway car hand brake mechanisms are well known and usually include a large, rotatable hand wheel mounted on a shaft which, through a gear train, can rotate a chain gear to apply tension on a chain that is secured at its distal end to a brake rigging of the railway car. As the hand wheel is rotated in a first direction (apply mode) the brakes are applied. To prevent rotation of the hand wheel in the second opposite direction, chain tension is opposed by a pawl that engages a ratchet wheel on the hand wheel shaft. Rotation of the hand wheel in a second opposite direction (release mode) is allowed by a clutch mechanism on the ratchet wheel.
The railway car brake may also be released by disengaging the pawl from the detent wheel (“quick release”), but this would cause rapid rotation of the hand wheel and the gears of the gear train. To avoid rapid rotation of the hand wheel, hand brake mechanisms have been devised which are known as “non-spin release” mechanisms and which include releasable connecting gears between the hand wheel shaft and the gear train. When the connecting gears are released, the gears of the gear train rotate rapidly, without constraint by the pawl and ratchet wheel, and the hand wheel remains stationary.
“Quick release” mechanisms use a handle to disconnect the gears between the hand wheel shaft and the gear train allowing the brake to release. However, if the quick release handle is allowed to return to the unreleased position, the gear shaft and gear train may be inadvertently reengaged before the brake fully releases. Therefore, in conventional quick release mechanisms, the operator must hold the quick release handle in the release position long enough to ensure that the brake fully releases.